iMac with Windows, black screen and no boot, what to do?

Question

Windows

Guys tell me, there was such a nuisance. iMac, when turned on, gives the sound of Apple and that's it, the download does not go any further. Just a black screen.
What happened before: there was Mac 10.9. It was necessary to install Windows. Installed Windows 10 through BootCamp, configured everything worked. Both Windows and Mac. Through Alt there was a choice of loading.
And once working in Windows, you had to reboot into Mac. I press restart and that's it. At startup, the Apple sound sounds and the download does not proceed further. Just a black screen. Pressing alt while loading does nothing.
In general, the problem turned out to be in the HDD. He is dead. It was changed and everything worked.

Answer 1

Try resetting the NVRAM. Immediately after turning on, press and hold the alt, cmd, r, p buttons. The Mac will reboot and start to boot from Mac OS, start responding to the alt button. If the reset does not help, then there is probably a problem with the hard drive. It happens that the hard dies so that it completely hangs up, it will not even respond to alt.

Answer 2

iMac you take in your bag, get dressed, go to the service,
- "Hello, ..."

Answer 3

Resetting NVRAM didn't help, but the problem persists. Looks like the hard drive came Khan. You can’t change the hard drive on an iMac just like that, you have to go to a service to replace the drive. And then even Alt does not react when loading. Although the nvram reset is fine.